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Squaliformes
The dogfish sharks, '''or '''Squaliformes are an order of sharks that includes about 126 species in seven families. Members of the order have two dorsal fins, which usually possess spines, no anal fin or nictitating membranes, and five gill slits. In most other respects, however, they are quite variable in form and size. They are found worldwide, from polar to tropical waters, and from shallow coastal seas to the open ocean. Notable species in this family include the Greenland shark, piked dogfish, viper dogfish and others. Classification There are six families of squaliformes currently in existence. Family Centrophoridae (gulper sharks)- The gulper sharks are usually deepwater fish. While some, such as the gulper shark Centrophorus granulosus, are found worldwide and fished commercially, others are uncommon and little-known. Their usual prey is other fish, though some are known to feed on squid, octopus, and shrimp. Some species live on the bottom (benthic), while others are pelagic. They are ovoviviparous, with the female retaining the egg-cases in her body until they hatch. They are small to medium sharks, ranging from 79 centimetres (2.59 ft) to 164 centimetres (5.38 ft) in adult body length. * Genus Centrophorus * Genus Deania Family Dalatiidae '(kitefin sharks)- Kitefin sharks are small squaliformes, under 2 m (6.6 ft) long, and are found worldwide. They have cigar-shaped bodies with narrow heads and rounded snouts. Several species have specialized bioluminescent organs. The term ''kitefin shark is also used as the common name for the type species of the family, Dalatias licha. Notable members of this family include the infamous cookie-cutter shark (Isistius brasiliensis). * Genus Euprotomicroides * Genus Heteroscymnoides * Genus Mollisquama * Genus Dalatias * Genus Isistius * Genus Euprotomicrus * Genus Squaliolus '''Family Echinorhinidae (bramble sharks)- Bramble sharks are usually benthic fish found in tropical and temperate waters worldwide, while the prickly shark is found in the deep waters of the Pacific Ocean. Their usual prey is small fish, cephalopods, and crustaceans. They are ovoviviparous, with the female retaining the egg cases in her body until they hatch. They are relatively large sharks, ranging from 3.1 to 4 metres (10 to 13 ft) in adult body length. * Genus Echinorhinus Family Etmopteridae (lantern sharks)- Lantern sharks are deepwater fish with light-producing photophores on their bodies. The members of this family are small, under 90 cm (35 in) long, and are found worldwide. * Genus Aculeola * Genus Centroscyllium * Genus Etmopterus * Genus Trigonognathus Family Oxynotidae (rough sharks)- Rough sharks are characterised by two large dorsal fins, each with a sharp spine, and with the first fin placed far forward above the head. Their bodies are compressed, giving them a triangular cross-section. Their skins are even rougher and more prickly than the dogfishes (below). Rough sharks are small to medium in size, ranging from 49 to 150 centimetres (1.61 to 4.92 ft) in adult body length, depending on species. They are deepwater sharks possessing a luminous organ which live in Atlantic and western Pacific oceans. * Genus Oxynotus Family Somniosidae (sleeper sharks)- Sleeper sharks are a poorly studied deep-sea shark found in all oceans. They contain antifreeze to survive in cold temperatures, and may feed on colossal squid. In Iceland, they are hunted for food. They are allowed to rot for months until the poisonous antifreeze degrades, and they are safe to eat. The Greenland shark, the longest-lived shark and vertebrate currently known to science, is a member of this family. * Genus Centroscymnus * Genus Centroselachus * Genus Scymnodalatias * Genus Scymnodon * Genus Somniosus * Genus Zameus Family Squalidae (dogfish sharks)- Dogfish sharks have two dorsal fins, each with smooth spines, but no anal fin. Their skin is generally rough to the touch. These sharks are characterized by teeth in upper and lower jaws similar in size; caudal peduncle with lateral keels; upper precaudal pit usually present; and a caudal fin without a subterminal notch. Unlike nearly all other shark species, dogfish possess venom as a defensive measure against predators, which coats their dorsal spines and is mildly toxic to humans. Their livers and stomachs contain also the compound squalamine, which possesses the property of reduction of small blood vessel growth in humans. * Genus Cirrhigaleus * Genus Squalus Category:Chondrichthyes Category:Elasmobranchs Category:Sharks Category:Squaliformes